The present invention relates to a nonvolatile memory device integrated with a voltage booster.
Generally, rewriting of the nonvolatile memory requires a high operating voltage, for example, about 20V. FIG. 3 shows the performance of a voltage booster, where the voltage booster cannot generate a desired high voltage when the power source voltage falls below a certain level, for example, 2.5V. Therefore, the nonvolatile memory cannot effect a rewriting operation under such a level of the power source voltage. In view of this, as shown in FIG. 2, conventionally a power source voltage detection circuit is utilized and is always operated so as to forcibly inhibit operation of the voltage booster when the detection circuit detects that the power source voltage falls below a certain level, for example, 3.0V even if an enabling signal has been generated to operate the booster, thereby preventing erroneous or insufficient rewriting of the nonvolatile memory.
The power source voltage detection circuit includes a constant voltage circuit 1 operative to apply a constant voltage V.sub.a to a gate electrode of P channel transistor 10 to enable the same to flow a constant I.sub.10. Then, a circuit 2 applies a voltage V.sub.b dependent on the power source voltage or supply voltage to a gate electrode of N channel transistor 11. When the supply voltage is in a lower level, the N channel transistor 11 is turned off to hold a node A at "H" level. Therefore, an output B of the supply voltage detection circuit is held at "L" level. On the other hand, when the supply voltage exceeds a given level, the N channel transistor 11 is turned on to lower the voltage level of node A below an inversion voltage of inverter 3. Consequently, the output B of the supply voltage detection circuit is turned to "H" level. As a result, when the supply voltage is below the predetermined level, the output of the supply voltage detection circuit is held at "L" level. Therefore, an input C of the booster is held at "L" level effective to inhibit operation of the booster even if a control signal is turned to "H" level so as to enable the booster.
However, the conventional supply voltage detection circuit is always maintained in an operating state even during other than a necessary duration of boosting operation, thereby causing the drawback that unnecessary current is consumed.